GREENHOUSE LIGHTING

1 GREENHOUSE LIGHTING Neil Mattson, Associate Professor and Floriculture Extension Specialist Cornell University, 134A Plant Science Building, Ithaca, NY 14853 email: phone: (607) 255-0621 3 ways to think about light Light quantity also referred to as light intensity, is the total amount of light supplied to the plant, which is then used for photosynthesis; up to a point the higher light quantity the more energy a plant can sequester in photosynthesis Light quality refers to the wavelengths of light supplied ( color of light), for example red light has wavelengths between about 630-700 nanometers, far red light is 705-740 nm, blue light is at 400-450 nm, and ultraviolet A is 315-400 nm. Plants can respond to different colors of light by changing their growth form (phytomorphology) a high fraction of far-red light (from incandescent lamps or as shaded by other plants) causes plants to stretch excessively.

2 . Measure of light f or plants (400 to 700 nm): • Photosynthetically Active Radiation (PAR), this is measured in the range of 400-700 nm o The unit for measuring instantaneous light incident upon a surface is micromoles per square meter per second (or µmol/m2/s) - this is the amount of energy (photons or particles of light ) hitting a square meter every second.

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